[tex]\boxed{P.V = n.R.T}[/tex]
[tex]P = ?\ atm\\\ T = 27+273 = 300\ K\\\\\\ n_1 =\frac{m}{MM}\\\\\ n =\frac{640}{32} = 20\ mol\\\\ R = 0,082\ atm \ L\ K\\\\ V = 82\ L[/tex]
[tex]P_1\cdot82 = 20\cdot0,082\cdot300\\\\ \boxed{P_1 = \frac{492}{82} = 6\ atm}[/tex]
Agora calculemos o número de mols no final:
[tex]1,5\cdot 82 = n_2\cdot0,082\cdot300\\\\ 123 =\ n_2\ 24,6\\\\ \boxed{n_2 = \frac{123}{24,6} = 5\ mol}[/tex]
Agora encontramos a massa de oxigênio.
[tex]n_2 = \frac{m_2}{MM_2}\\\\ 5 = \frac{m_2}{32}\\\\ \boxed{m_2 = 160\ g}[/tex]